Interactions of human T cell immunoglobin mucins with apoptotic cells.

T cell immunoglobulin mucin (TIM) family plays a key role in regulating immune responses. In this study, the interactions of human TIM family with apoptotic cells were evaluated in order to provide a foundation for further study on the roles of human TIM genes in apoptosis. Nine kinds of pEGFP-N1 eukaryotic expression vectors containing different lengths of the three members of human TIM genes for the expression of TIM-EGFP and the vectors for the expression of TIM-Fc fusion proteins were constructed. It was found that human TIM proteins could recognize and bind to apoptotic cells directly, but not to viable cells. The interactions of sTIM-1-EGFP, sTIM-3-EGFP and sTIM-4-EGFP with apoptotic cells were blocked by TIM-1-Ig, TIM-3-Ig and TIM-4-Ig fusion proteins respectively. In addition, human TIM proteins mediated the recognition of apoptotic cells and bound to apoptotic cells directly via the IgV domains. In conclusion, the TIM family may play a key role in the regulation of apoptosis. Our data also suggest that human TIM proteins probably serve as novel proteins for the detection of the early cellular apoptosis.